In the integrated interior of a house where the kitchen is not partitioned from but directly communicates with the living room or bed room, food smell lingers in the indoor air while cooking thus penetrating the whole house and furthermore penetrating neighboring houses. In the case of an apartment house, the food smell spreads to the corridor air. In this regard, while cooking, the family members and neighbors become upset. To prevent this problem, a pot with a cooling tub on the top of the pot lid was invented (U.S. Pat. No. 4,539,899). But this pot has a fault in that condensing efficiency is not sufficient because vapor heats the lid directly then returns to the inside of the pot.
To increase condensing efficiency, Lid type backward flow liquification means for cooking was invented and is disclosed in U.S. Pat. No. 4,539,899 and DE. P. 3213852.0. This cooker has two hollowed tubs combined with each other vertically and between the two tubs there is a circular current tube. The two tubs are filled with coolant, so heated vapor is cooled by the coolant while passing the circular current tube. Such liquification means, however, are expensive and hard to make.